Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Saturated Water
Name: Nick
Status: educator
Age: 30s
Location: N/A
Country: N/A
Date: 2000


Question:
One liter of air containing 4% water vapor by volume(saturated), contains how much liquid water?


Replies:
You could calculate this from the ideal gas equation of state, pV = nRT, where
p = atmospheric pressure,
V = volume of the sample (= 1 L in this case),
n = the number of moles of gas (unknown in this case),
R = the "universal gas constant," 0.0820575 L atm / (K mol),and
T = the temperature in K; room temperature is about 298 K.
   

Solving this equation for n tells you how many moles of gas are present. 4% of that is water. Knowing that water weighs 18 g/mole, you can then determine the weight of the water in the 1-L sample of air.

How can this be empirically demonstrated?

Two ways I can think of:

1. Put the sealed sample in a freezer, and weigh the frost that forms on the inside of the container.

2. Place a dessicant in the sealed sample container, and weigh the dessicant after it has absorbed all the water.

I have been unable to find this concept discussed in any chemistry references looked up so far. Perhaps you could direct me to a source where this is talked about.

Here's a really good intro:
http://pasture.ecn.purdue.edu/~tao/homepage210/useful/vapor_pr/sld001.htm

You might be able to get something out of these sites as well:
http://atmos.nmsu.edu/education_and_outreach/encyclopedia/humidity.htm
http://www.crh.noaa.gov/lmk/soo/docu/humidity.htm
http://www.uswcl.ars.ag.gov/exper/relhumeq.htm
http://www.chem.sunysb.edu/hanson-foc/lesson13.htm
http://library.thinkquest.org/12596/dalton.html
http://www.chem.ualberta.ca/~plambeck/che/p101/p01044.htm

There are many more! Just search on "partial pressure."

Richard E. Barrans Jr., Ph.D.
Assistant Director
PG Research Foundation, Darien, Illinois



Click here to return to the Chemistry Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (help@newton.dep.anl.gov), or at Argonne's Educational Programs

NEWTON AND ASK A SCIENTIST
Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory